Not too sure if I like roof layers on roof layers. Being "old technology" person and having DIY skills in many different areas, I'd rather strip its entire roof down to its studs, install more studs between its existing factory studs (to create 12" apart instead of its factory 24" apart), then install new 1/4" plywood. And, instead of installing EDP sheets (that shed and create black streaks), I'd install liquid rubber roof on the plywood surface. This liquid stuff (applied with brush / roller) doesn't create black streaks. I'd do above if I plan to keep RV/TT for 3+ years. If selling / trading RV/TT within 3 years, I'd apply liquid rubber roof only over its damaged roof area. Low cost fix for the short term. Your choice.